Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04W—WIRELESS COMMUNICATION NETWORKS
  • H04W52/00—Power management, e.g. Transmission Power Control [TPC] or power classes
  • H04W52/04—Transmission power control [TPC]
  • H04W52/30—Transmission power control [TPC] using constraints in the total amount of available transmission power
  • H04W52/36—Transmission power control [TPC] using constraints in the total amount of available transmission power with a discrete range or set of values, e.g. step size, ramping or offsets
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04W—WIRELESS COMMUNICATION NETWORKS
  • H04W52/00—Power management, e.g. Transmission Power Control [TPC] or power classes
  • H04W52/04—Transmission power control [TPC]
  • H04W52/18—TPC being performed according to specific parameters
  • H04W52/22—TPC being performed according to specific parameters taking into account previous information or commands
  • H04W52/225—Calculation of statistics, e.g. average or variance
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04W—WIRELESS COMMUNICATION NETWORKS
  • H04W52/00—Power management, e.g. Transmission Power Control [TPC] or power classes
  • H04W52/04—Transmission power control [TPC]
  • H04W52/18—TPC being performed according to specific parameters
  • H04W52/22—TPC being performed according to specific parameters taking into account previous information or commands
  • H04W52/228—TPC being performed according to specific parameters taking into account previous information or commands using past power values or information
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04W—WIRELESS COMMUNICATION NETWORKS
  • H04W52/00—Power management, e.g. Transmission Power Control [TPC] or power classes
  • H04W52/04—Transmission power control [TPC]
  • H04W52/18—TPC being performed according to specific parameters
  • H04W52/24—TPC being performed according to specific parameters using SIR [Signal to Interference Ratio] or other wireless path parameters
  • H04W52/241—TPC being performed according to specific parameters using SIR [Signal to Interference Ratio] or other wireless path parameters taking into account channel quality metrics, e.g. SIR, SNR, CIR or Eb/lo
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04W—WIRELESS COMMUNICATION NETWORKS
  • H04W52/00—Power management, e.g. Transmission Power Control [TPC] or power classes
  • H04W52/04—Transmission power control [TPC]
  • H04W52/18—TPC being performed according to specific parameters
  • H04W52/24—TPC being performed according to specific parameters using SIR [Signal to Interference Ratio] or other wireless path parameters
  • H04W52/247—TPC being performed according to specific parameters using SIR [Signal to Interference Ratio] or other wireless path parameters where the output power of a terminal is based on a path parameter sent by another terminal

Definitions

• the present invention relates to a method, radio base station and a mobile station for transmitting, receiving and using transmission power control commands.
• Power control and soft handover are two important functionalities of the Code Division Multiple Access (CDMA) air interface.
• Power control is used to continuously adjust transmission power such that the perceived quality is sufficiently but not excessively good. By controlling transmission power in this manner it is ensured that not more than necessary interference is generated, which in turn results in that the system performance can be improved.
• the inner loop power control adjusts transmission power so that the Signal to Interference plus Noise Ratio (SINR) perceived by the receiver is close to a SINR target set for the receiver.
• the inner loop power control is typically implemented by sending power control commands via so called Transmission Power Control (TPC) bits.
• TPC Transmission Power Control
• the power control command is obtained at the transmitter by comparing the received SINR with the SINR target. To increase the transmission power the TPC bit indicates "up” and to decrease the transmission power the TPC bit indicates "down”.
• the uplink power control command is sent via downlink dedicated physical control channel (DPCCH) for High Speed Downlink Package Access (HSDPA) incapable User Equipment (UE) and associated dedicated physical channel (A- DPCH) or fractional dedicated physical channel (F-DPCH) for HSDPA capable UE.
• DPCCH downlink dedicated physical control channel
• HSDPA High Speed Downlink Package Access
• UE User Equipment
• A- DPCH dedicated physical channel
• F-DPCH fractional dedicated physical channel
• the outer loop power control adjusts the SINR target so that the desired Quality of Service (QoS) requirement is met.
• QoS Quality of Service
• a mobile station also termed user equipment (UE) is in the overlapping cell coverage area of more than one base station.
• UE user equipment
• the communication between the mobile station and base stations takes place concurrently via all connected radio links.
• Soft handover is a way to decrease the dropping probability when a mobile station moves from one cell to another cell.
• one mobile station is connected to two or more base stations and is power controlled by all the base stations to which the mobile station is connected.
• Each connected base stations transmits a power control command to the mobile station.
• the mobile station typically combines the received power control commands from all the base stations in the following way:
• a mobile station in soft handover will more likely decrease its transmission power when the received power control commands are unreliable since any unreliable power control command that is misunderstood as "down" will lead to that the mobile station decrease the transmission power.
• the transmission power may be decreased when it should have been increased. Too low uplink power can lead to bad uplink quality.
• a TPC discarding mechanism can be employed, as is described in Niclas Wiberg, Hu Rong, Fredrik Gunnarsson, Bengt Lindoff, "Combining of Power Control Commands During Soft Handover in WCDMA", PIMRC2003 .
• the reliability of received TPC bit can be checked before power control commands are combined.
• Unreliable TPC commands i.e. the TPC commands with error probability greater than a predefined threshold, are discarded and only the reliable TPC commands are combined. In the case when all TPC commands are discarded, the transmission power is kept the same, neither increases nor decreases, which is referred as "hold".
• the TPC discarding mechanism solves the problem of risking a too low uplink quality caused by unreliable TPC commands. However, the TPC discarding mechanism may cause other problems.
• FIGS Ia - Ib One example of such a problem is illustrated in Figures Ia - Ib.
• EUL Enhanced Uplink
• UE User Equipment
• FIG. 1a The plots in figure Ia are the rise over thermal (RoT) averaged over one sub-frame in the serving and the non-serving cells of the UE.
• RoT rise over thermal
• the upper plot is the SINR of the best A-DPCH in the Active Set (AS) while the lower plot of figure Ib is the SINR of the second best A-DPCH in the AS.
• the TPC power offset relative to the pilot bits carried by A-DPCH is 3 dB.
• a high RoT pulse will also cause an uplink power rush for users who are not in soft handover.
• Such a high and short RoT pulse is difficult for Uu load control to reduce via a Node B scheduler since there are measurement and operation delays.
• One solution is to increase the reliability of TPC by setting a higher quality target for the relevant downlink channel carrying the uplink TPC command, for example the A-DPCM.
• the transmission power on TPC bit can be increased by increasing the TPC power offset, which is supported in 3GPP.
• the TPC power offset can be varied from 0 dB to 6 dB, see 3GPP TS 25.331, "Radio Resource Control (RRC)", v.7.4.0.
• RRC Radio Resource Control
• Dynamical setting of TPC power offset based on some relevant quality is supported in 3GPP, see 3GPP TS 25.214, "Physical layer procedures (FDD) ", v.7.4.0 by signaling the quality measurement, see 3GPP TS 25.433, “UTRAN Iub interface Node B Application Part (NBAP) signaling) ", v.7.5.0. Also, in WO2006/081874 a method to adjust the TPC power offset was proposed, where the TPC power offset is increased based on an event triggered report from user in the case when a number of M unreliable TPC commands are registered during a given time period.
• FDD Physical layer procedures
• NBAP UTRAN Iub interface Node B Application Part
• TPC power offset can for example be based on an estimated uplink Dedicated Physical Control CHannel (DPCCH) SINR at the radio base station, the number of TPC "up” and the number of TPC "down” sent by a radio base station and aggregated UE receiver power or UE transmit power over a number N slots.
• DPCCH Dedicated Physical Control CHannel
• a mobile station used in a cellular radio system supporting soft handover may also be adapted to apply TPC discarding thresholds based on the number and the quality of simultaneously received TPC commands.
• the discarding procedure in the mobile station may also be carried out selectively such that TPC commands that are determined to be unreliable are not discarded but selectively discarded based on how reliable they are determined to be.
• FIG. Ia and Ib are views illustrating variation of different parameters in a cellular radio system
• - Fig. 2 is a view of a cellular radio system
• - Fig. 3 is a flow chart illustrating different steps performed when adjusting transmitting power control commands in a node of a cellular radio system
• - Fig. 4 is a flow chart illustrating different steps performed when discarding power control commands in a user equipment for use in a cellular radio system.
• a general view of a cellular radio system 200 is shown.
• the system 200 comprises a number of cells 201 together covering a geographical area in which the system 200 provides radio access.
• Each cell 201 is associated with a radio base station 203, which communicates with a Radio Network Controller (RNC) 205.
• the RNC is in turn connected to a Core Network (CN) 207.
• CN Core Network
• UE user equipment
• UE 209 may connect to the cellular radio system via a radio base station 203 over an air- interface.
• the cellular radio system and the mobile station support soft handover the UE 209 may be connected to more than one radio base station 203 simultaneously.
• the power offset of a Transmission Power Control (TPC) command is adjusted depending on some available measurements which reflect the quality of the downlink channel carrying the uplink TPC command.
• the adjustment is preferably performed at a radio base station (RBS) 203.
• Some measurements can be derived at the base station and some may be derived by a mobile station connected to the radio base station and transmitted as feedback from a mobile station to the radio base station.
• Measurements that can be derived at the base station include:
• N may be a configurable parameter.
• the received UE power can be regarded as "hold” in one slot if the difference between the received UE power in this slot and that in the previous slot is very small.
• the received UE power can also be obtained via the existing UE measurement reports, see 3GPP TS 25.215, “Physical layer measurements (FDD) ", v.7.4.0, where the transmission power of the mobile station and power headroom of user are estimated in the mobile station/user equipment and reported back to the radio base station.
• FDD Physical layer measurements
• Measurements can, as stated above, also be performed at a mobile station.
• a mobile station/user equipment can be adapted to examine and report accumulated changes in transmission power back to the radio base station. Such reporting may involve procedure as described below:
• the system can be adapted to determine and configure when a mobile station/user equipment starts to examine the changes in transmission power.
• the mobile station/user equipment may be configured to decide when to start the examination on the transmission power then report to the system.
• the report can be sent either periodically or be event triggered.
• the measurement report may include: at least one of the following
• the trigger event may for example be when the accumulated increase in UE transmission power is more than a predetermined amount x dB or when the UE transmission power has been held for more than m out of N slots.
• This report from the mobile station/user equipment can be transmitted back to the radio base station using either RRC signaling or some lower layer, e.g. layerl, Iayer2, or Media Access Control (MAC) signaling or some other suitable signaling channel available to the mobile station/user equipment.
• RRC signaling or some lower layer, e.g. layerl, Iayer2, or Media Access Control (MAC) signaling or some other suitable signaling channel available to the mobile station/user equipment.
• MAC Media Access Control
• the measurement made available to a radio base station is processed at each base station to obtain measurements that reflect the quality of the downlink channel carrying the uplink TPC commands.
• at least one of the following measurements are obtained:
• each base station may increase the power offset on TPC command if any of the following conditions is satisfied depending on available measurements and post-processed measurements and where N may be a configurable parameter:
• the base station can estimate at least how much decreasing in UE power is expected if the TPC commands are correctly received at the mobile side. If the accumulated decreasing in user power is less than what is expected and the difference exceeds a certain margin, the power offset on TPC command is increased, or
• each base station may be set to decrease the power offset on TPC commands if the number of slots that UE power is "hold" over last N slots is less than a certain threshold and if:
• the estimated uplink DPCCH SINR is lower than the DPCCH SINR target plus a margin or
• the number of TPC "down" commands that is sent from the base station is not more than a predefined margin over the number of TPC "up” commands. Note that the margin (threshold) used to trigger decrease on TPC power offset can be different from the margin (threshold) used to trigger increase on TPC power offset.
• a TPC power offset may also be adjusted based on Common Pilot Channel (CPICH) quality either in terms of CPICH Ec/Io or CPICH Received Signal Code Power (RSCP).
• CPICH Common Pilot Channel
• RSCP CPICH Received Signal Code Power
• the CPICH quality based TPC power offset adjustment may be combined with the TPC power offset adjustment proposed in section described above in various ways: For example, for each UE the Radio Network Controller (RNC) can be set to adjust the uplink TPC power offset for each radio base station in the active set of that UE based on the CPICH quality reported by the UE and send the uplink TPC power offset to the radio base stations. Each radio base station may further adjust the uplink TPC power offset received from the radio network controller according to any criteria described above.
• RNC Radio Network Controller
• an upper bound and a lower bound may be applied on the TPC power offset per radio link set.
• the upper bound is set to prevent the TPC power offset becoming too large and resulting in an unnecessary high transmission power. It should be noted that the upper bound can be different for each radio link set and some of them can be higher than 6 dB if it is necessary.
• a flowchart illustrating the procedural steps performed when adjusting the power offset of a TPC command is shown.
• measurements relating to the quality of the downlink channel carrying the uplink TPC command are obtained.
• the measurements may be direct measurements at the radio base station 203 or reports from some other entity such as a mobile station 209.
• a TPC power offset is determined based on the obtained measurements.
• the offset determination can for example be determined in accordance with any of the procedures outlined above.
• the TPC power offset is then adjusted, i.e. increased, decreased or kept the same based on the determined power offset in step 303 in a step 305.
• the TPC commands are transmitted using the adjusted power offset in a step 307.
• a Transmission Power Control commands may be selectively discarded by the user equipment.
• TPC command discarding is to avoid that the uplink quality drops as a result of many unreliably TPC commands received at a user terminal.
• a TPC command is considered to be unreliable when the probability that the terminal cannot correctly interpret the TPC command is above some, high, probability.
• TPC command discarding has less impact on performance for non- soft handover users, in which only one TPC command is received at mobile station. This is because the fact that the probability that one TPC command is incorrectly received is much lower than the probability that at least one TPC command out of N TPC command (N>1) is incorrectly received given that all the TPC commands have the same error probability.
• N the probability that at least one TPC command out of N TPC command (N>1) is incorrectly received given that all the TPC commands have the same error probability.
• N the probability that at least one TPC command is incorrectly received
• a procedure involving a selective TPC command discarding for the case when there are more than one TPC commands received at user terminal may be used.
• the selective TPC command discarding procedure is configured such that the TPC discarding threshold is based on the number of TPC commands that the discarding criteria are evaluated on. In fact this may result in the discarding threshold is relaxed allowing a higher TPC error rate when there are only a few unreliable TPC commands.
• the selection of TPC discarding may be set as follows when a user terminal receives NTPC commands simultaneously: - Discard all the N TPC commands if all the TPC commands have an error rate higher than a preset discarding threshold Thr n - Otherwise discard the N-I TPC commands if they all have an error rate higher than the discarding threshold Thr n- i
• Thrd lsC ard ⁇ The thresholds setting depends on UE implementation.

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• Engineering & Computer Science (AREA)
• Computer Networks & Wireless Communication (AREA)
• Signal Processing (AREA)
• Physics & Mathematics (AREA)
• Probability & Statistics with Applications (AREA)
• Quality & Reliability (AREA)
• Mobile Radio Communication Systems (AREA)

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• 2008
  • 2008-01-29 WO PCT/SE2008/050112 patent/WO2009096830A1/en not_active Ceased
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  • 2008-01-29 US US12/864,668 patent/US8385969B2/en active Active
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